The invention relates to new nitrogen-containing additives for use as depressants of the cloud point of middle hydrocarbon distillates (fuel oils, gas oils), as well as to compositions of middle distillates containing said additives.
The petroleum distillates concerned by the invention consist of middle distillates (fuel oils, gas oils) whose distillation range (standard ASTM D 86-67) is between 150.degree. C. and 450.degree. C. The more particularly concerned gas oils have a distillation interval ranging from an initial temperature between 160.degree. and 190.degree. C. to a final temperature between 350.degree. and 390.degree. C.
A great number of products have been marketed, aiming to improve the limit filterability temperature and the pour point of petroleum cuts of high paraffin content, such as, for example:
polymers based on long chain olefins, PA0 copolymers based on alpha-olefins, PA0 ethylene-vinyl acetate copolymers, PA0 N-acylaminoethyl esters of acid-containing polymers, or PA0 halocarbon compounds. PA0 (A) recurrent units derived from vinylic or acrylic esters, PA0 (B) recurrent units derived from diisobutylene, and PA0 (C) recurrent units derived from an unsaturated .alpha.,.beta.-dicarboxylic compound. PA0 10 to 90%, preferably 15 to 70%, by mole, of recurrent units (A) (derived from vinyl esters or acrylic esters). PA0 5 to 40%, preferably 15 to 40%, by mole, of recurrent units (B) (derived from diisobutylene). PA0 5 to 50%, preferably 15 to 45%, by mole, of recurrent units (C) (derived from an .alpha.,.beta.-unsaturated dicarboxylic compound).
These products act on the kinetic and crystallization phenomena and modify the size of the crystals, allowing the use of the suspension at a lower temperature without plugging of the pipes and filters. The above products do not modify the temperature at which the first paraffin crystals appear. As a matter of fact, it has been considered up to now that this temperature was a datum depending on the molecular weight and the formula of the paraffins and on the nature of the solvent.
Decreasing the cloud point of middle distillates (particularly gas oils) by means of an additive would be very advantageous to the refiners since it would make it possible, without modification of the distillation flow sheet, to meet the specifications which tend now to be more and more severe.
It has now been discovered that certain chemical compounds, whose definition is given hereunder, have the property, when added to middle distillates, to cause the first paraffin crystals to appear at a temperature lower than that at which these crystals appear in the absence of these additives. This property is the more unobvious as it is retained after several heating and cooling cycles and it results from a yet unexplained mechanism.
This class of chemical compounds also has an effect on other properties of middle distillates (particularly gas oils), by modifying the behavior of the medium containing the settled paraffins.
Thus, the compounds of the invention have an important effect on the limit filterability temperature and the pour point.
When paraffin crystals, whose formation results from cooling, have appeared, their normal tendency is to gather by gravity at the bottom. This phenomenon, usually known as sedimentation, results in the plugging of ducts and filters and is detrimental to an accurate use of middle distillates, particularly of gas oils. The chemical compounds of the invention can substantially reduce the settling rate of the paraffins formed by cooling of gas oils and other middle distillates.
Finally, the products of the invention, which possess the above properties, also impart to gas oils and middle distillates to which they are added anti-corrosion properties towards metal surfaces.
The use of certain copolymers as additives decreasing the pour point of a number of hydrocarbon oils, particularly middle distillates, such as gas oils and fuel oils, has been described in the published French patent application No. 2 471 405. These copolymers consisted particularly of terpolymers formed of:
The latter consisted of anhydrides, dicarboxylic acids, diesters or imides N-substituted with hydrocarbon radicals, optionally further comprising at least one amine group and/or at least one hydroxy group. The N-substituted imide elements illustrated in this patent application resulted chiefly from the condensation of N,N-dimethyl 1,3-propane diamine on vicinal anhydrides, diacids or diesters groups present in the terpolymer.